Microporous polymers are polymers having pore sizes typically ranging from less than 1 micrometer (μm) to a few micrometers in diameter. Microporous polymers are useful in a variety of applications. For example, microporous polymers are often used in electronic devices (such as battery separators, capacitor separators, electrode binder materials, sensors, etc.), and as filtration materials (for example in separating gases, ions, and/or liquids), fabrics, mats, cloth, fibers (including hollow fibers), structural foams, and other applications that are well known to one skilled in the art.
Unfortunately the porosity, i.e., the amount of voids or interstitial space, of most conventional microporous polymers is limited, thereby reducing their usefulness. For example, batteries are used as an electricity source in a wide variety of applications. Batteries have an anode and a cathode that is separated by a separator (i.e., battery separator). The principal function of the battery separator is to prevent electrical conduction (i.e., “shorts”) between the anode and the cathode while permitting ionic conduction via the electrolyte. The pores of the separator are filled with an ionically conductive electrolyte and allow migration of electrolyte from one electrode to another. Since the pores of battery separators are conduits of power, batteries having high porosity separator(s) provide a higher battery power and/or a longer battery life. In some cases, battery separators also need to provide good mechanical properties, e.g., in dry batteries, for winding and low electrical resistivity for device performance.
Therefore, there is a continuing effort to produce microporous polymers having a higher porosity and ionic conductivity.